An electrical machine such as a generator can have a large field (usually the rotor), to which a corresponding large number of permanent magnets or poles is attached. During manufacture, each magnet must be firmly attached to the rotor so that it cannot come loose during operation. For a rotor with a diameter in the range of 2-6 m, a magnet can typically be 1-3 cm in height and 10-20 cm wide. A permanent magnet usually comprises a number of magnet pieces, each with a weight in the region of 10-15 kg. Prior art methods of mounting magnets usually involve attaching each magnet to a steel base of the same width as the magnet, for instance using an adhesive layer, and attaching this unit to the rotor by covering it with a U-shaped steel housing and soldering each housing along its lower edges onto the rotor. The housings ensure that the magnets are protected from corrosion and from mechanical impact. However, this approach is inflexible and expensive, since it requires a steel base for each magnet, a closely-fitting housing for each magnet, and a time-consuming soldering step. Another disadvantage is the additional weight contribution on account of the steel bars.
In an alternative approach, the magnets can be attached to the rotor by gluing them into place, and then wrapping the rotor and magnet arrangement in a fibreglass bandage or envelope. While this solution is considerably more economical than the other prior art technique, it does not provide satisfactory protection against corrosion or mechanical impact.